The researchers of the study suggest that there may be a dose-response relationship between carbohydrate consumption during exercise and immune response. Because of the advent of “light” sports drinks with low sugar content, the researchers wanted to know if there would be a difference in immune response between a standard sports drink, a light sports drink, and plain old water.

Study Design

Each participant completed an 18km to 20km run at seventy percent of their VO2 max three times, with a week in between the runs. Each time they drank from a one-liter bottle that contained one of the following three beverages:

In one of the runs, the drink was a seven-percent solution of carbohydrates (70g of carbs).

In another the drink was a light sports drink consisting of 1.5% carbohydrates (15g of carbs).

The final trial was just flavored water.

Before and after each race, blood was drawn to determine immune response. The researchers were looking for markers of stress and immune response, such as the hormone cortisol and the cytokine interleukin-6. They also directly examined several types of white blood cell counts.

Results

As expected, there was no difference in performance. In fact, there was only a minute difference between each of the three trials. With a test length of over an hour and a half, that’s some pretty amazing consistency. Heart rate was highest in the high-carb group, although not significantly. This was perhaps due to increased energy need for digestion.

There were, however, significant differences in immune response. The expected dose-response was pretty much on point. The 1.5% solution seemed to help a little, but was largely the same as the flavored water. However, the seven-percent solution had a markedly reduced immune response.

The authors concluded that carbohydrate consumption should be utilized during distance running events. The ideal rate is about 45g per hour, which is the rate at which it was consumed in the seven-percent solution. The purpose, as we have seen, is not to improve performance in the short term, but rather to mitigate the need for immune response.

Another Interpretation

Let me offer an alternative possibility. It is likely that the researchers are correct, and the reduced immune response is due to reduced stress via carb consumption. However, based solely on these results, it’s also possible the carbohydrate simply reduced the specific response studied by the researchers, without actually decreasing the stress. This alternative conclusion would still be consistent with the results.

The end goal, the researchers say, is to help prevent future infections by less exposure to stress. There is no doubt that the immune response was reduced in the higher carbohydrate group. The goal of reduced infections would seem to be supported by the results of this study, but since the rate of infections was not studied, it’s hard to say. You might also expect that performance would increase with better immune response, but it did not.

One thing is for sure: performance is unaltered by high-carb intake in the short term. Whether or not carb consumption during endurance training is actually beneficial has yet to be seen, but this evidence is a step in the right direction.